This invention relates to an epoxy resin composition for producing a resin plate by casting, a resin plate and a transparent resin plate for liquid crystal displays which are obtained by curing the epoxy resin composition, and a liquid crystal display comprising the transparent resin plate.
The transparent resin plate of a liquid crystal cell of a liquid crystal display (hereinafter xe2x80x9cLCDxe2x80x9d) has been made of thermoplastic resins or thermosetting resins as a substitute of glass. Thermosetting resins have been preferred for their heat resistance, optical anisotropy, and the like. The thermoplastic resins for this use mainly include liquid epoxy resins, which are cast molded to produce the resin plate.
Since cast molding has low production efficiency and is unsuited to large-volume production, it has been demanded to improve the production efficiency by adopting casting, which comprises spreading a liquid resin on a smooth endless belt made of stainless steel to produce sheeting in a continuous manner. However, where a conventional liquid epoxy resin that has been used in cast molding is applied to casting, the resin, having a low viscosity, flows more than needed to result in considerable variation in thickness of resulting sheeting. Thickness variation of a transparent resin plate used in an LCD causes fatal defects of display functions, such as color unevenness or luminous intensity unevenness.
Besides, casting has been employed for making sheeting of thermoplastic resins. There has been no report on production of an epoxy resin plate by casting. Conventional epoxy resin compositions include the above-described low-viscosity liquid ones which are used in cast molding, potting or printing and solid ones having no flowability at room temperature which are used as a transfer molding material for, for example, sealing of semiconductor devices, but an epoxy resin composition suitable for manufacturing resin plates by casting is unknown.
An object of the present invention is to provide an epoxy resin composition which can be cast to produce a resin plate and a transparent resin plate for an LCD (hereinafter inclusively referred to as a resin plate) which have satisfactory thickness precision.
Another object of the invention is to provide a resin plate produced from the epoxy resin composition.
Still another object of the invention is to provide an LCD having the transparent resin plate.
The above objects of the invention are accomplished by an epoxy resin composition whose viscosity at 25xc2x0 C. is from 50 to 400 P (poise).
The epoxy resin composition according to the present invention provides by casting a resin plate with markedly improved thickness precision. A transparent resin plate prepared by casting the epoxy resin composition provides an LCD exhibiting excellent display characteristics.